Composite carbon black particles

The present invention relates to specific carbon black particles modified by nano-sized inorganic compounds, a process for their preparation and their use as pigments.

Carbon black (Color Index (C.I.) Pigment Black 7) as one of black colorant is cheap in price and excellent performance characteristics such as high blackness as well as durability, but also serious disadvantages such as low dispersibility of very fine particles, high absorption in the UV region for photolithography and, as its nature, high electric conductivity under a high loading level in black compositions, which are not suitable in some special applications such as black matrix for high light-shielding devices. Therefore, a serious need in the market for carbon black added at a very high loading level to pursue a high optical density and meanwhile a good rheology, a same level of electrical insulation as organic matrix, especially properties maintenance after a high temperature baking are concomitantly demanded.

Plenty of efforts have been made to achieve and or improve blackness of carbon black when it is used as pigment in coating, printing and inks, adhesives, sealants, leathers and plastics. However, how to concomitantly improve a good bluish undertone is an issue that still remains open.

Various approaches over the last decades have been reported to decrease the electrical conductivity of carbon black meanwhile attempts to maintain its high optical density by surface treatment or compositions.

EP 0871540 B1 (CABOT) discloses modified carbonaceous materials in particular carbon black as one component of gel for one of applications purpose of electrical insulation. The way to treat carbon black is via reacting with a diazonium salt in a liquid medium to attach at least one organic group onto carbon surface, in essence referring to the patent entitled “Reaction of carbon black with diazonium salts, resultant carbon black products and their uses”. Such modified carbon blacks known to those skilled in the art that organic chemical groups are attached to the surface of carbon black. For example, the modified carbon black can be prepared using the methods described in U.S. Pat. Nos. 5,554,739, 5,707,432, 5,837,045, 5,851,280, 5,885,335, 5,895,522, 5,900,029, 5,922,118, and 6,042,643, and PCT Publication WO 1999 023174 A1 and EP 0904327 B1, EP 0906371 B1, EP 1007595 B1. Such methods provide for a stable attachment of the groups onto the carbon black compared to dispersant type methods, which use, for example, polymers and/or surfactants. Other methods for preparing the modified carbon black include reacting a carbon black having available functional groups with a reagent comprising the organic group, such as is described in, for example, U.S. Pat. No. 6,723,783 or in the references incorporated above. In addition modified carbon blacks containing attached functional groups may also be prepared by the methods described in U.S. Pat. No. 6,831,194 and 660,075, EP 1252237 B1. Patent Publication Nos. 2003-0101901 and 2001-0036994, European Patent No. 1 394 221, and PCT Publication No. WO 04/63289. In addition EP 1600473 A2 (CABOT) discloses a modified pigment inclusive of carbon black attached at least one photopolymerizable group and at least one ionic or ionizable group. Compositions comprising such treated carbon black can be used for black matrix. And EP 1737916 B1 (CABOT) discloses modified carbon black by virtue of covalently attached organic group onto surface of carbon black is to enhance electrical insulation properties for PEMs use.

EP 1136526 B1 (DEGUSSA) refers to carbon black with organic groups in which the organic groups are linked to the black via a sulfide- and/or polysulfide bridge. Furthermore, a method of producing the black of the invention is described in which carbon black and compounds of the general formula R—S y—R are reacted. The carbon blacks can be used as filler, UV stabilizer, conductivity black and pigment.

WO 2009 025297 A1 (MITSUBISHI) discloses a resin black matrix comprising at least three to five organic colored pigments selected from red, blue, green, yellow, violet and orange pigments, but such a multiple pigment combinations do not give a sufficiently high optical density. Organic black pigments have also been widely proposed, for example perylene black, such as C.I. Pigment Black 32 etc., however, such previously known organic black pigment have the disadvantages of maintain a high jetness particularly after a high thermal baking.

WO 2012 051264 A1 (CABOT) discloses a black matrix using a mixture of surface modified C.I. Pigment Black 32 and a polyoxyalkylene polymer modified carbon black. In order to attain a sufficient optical density a high amount of modified carbon black is required, which adversely increase the electric conductivity.

EP 1484366 B1 (SAKATA) refers to a pigment produced by treating at least one pigment selected from the group consisting of organic pigments and carbon black each having a functional group reactive with a carbodiimide group with a carbodiimide compound having one or more carbodiimide groups, said carbodiimide compound having, within the molecule thereof, at least one side chain selected from the group consisting of polyester side chains, polyether side chains and polyacrylic side chains, with a carbodiimide equivalent of 100 to 50,000.

EP 2025723 B1 (TOKAI CARBON) discloses a hydrophilic carbon black that is suitable for an aqueous ink and useful for materials used for which the high resistivity and high light blocking properties required. Therein by subjecting the carbon black to either liquid-phase oxidation or gas-phase oxidation.

WO 1997 000295 A1 (NIPPON SHOKUBAI) discloses a resinous compositions containing carbon black by grafting a copolymer to carbon black surface to fulfill a satisfactory curing property and a stable dispersibility of carbon black. However the thermal durability reserved to keep the demanded performances.

WO 2004 020533 A1 (COLUMBIAN CHEMICALS) provides a method for the preparation of carbonaceous materials comprising a plurality of gamma-keto-carboxyl containing functional groups surface bonded thereto, and further provides several surface modified carbonaceous materials resulting therefrom.

WO 2004 063289 A1 (COLUMBIAN CHEMICALS) relates to the surface modification of various carbonaceous materials, compounds and compositions. More specifically, the invention provides methods for introducing amide functionality on to the surface of carbonaceous materials, compounds and compositions, and similarly provides several surface modified carbonaceous materials resulting therefrom.

WO 2008 146410 A1 (TOKAI CARBON) claims a dispersible surface-modified carbon black that is surface-modified by causing a functional group on the surface of the carbon black to be bonded to a diol-modified end-containing polymer through a triisocyanate compound exhibits excellent dispersibility in a non-polar solvent, a low-polar solvent, and a resin. The dispersible surface-modified carbon black is characterized in that a surface functional group of the carbon black is bonded to one isocyanate end group of a triisocyanate compound having three isocyanate end groups, and the remaining two isocyanate end groups are respectively bonded to hydroxyl groups of a diol-modified end-containing polymer.

U.S. Pat. No. 9,359,483 B2 (INDUSTRIAL TECHNOLOGY RESEARCH) refers to a hybrid carbon black, a coating composition, and a shielding material employing the same are provided. The hybrid carbon black includes a core of carbon black, and a cross-linked network polymer film covering the whole surface of the carbon black overall. In particular, the carbon black core has a mass fractal dimension between 2 and 3 and a surface fractal dimension between 2 and 2.5, and the cross linking network polymer film includes a product obtained by crosslinking a composition including a styrene monomer and a divinylbenzene monomer.

US 2012 0248383 A1 (ATANASSOVA) relates to a lead/sulfuric acid-based battery. Specifically claimed is a paste with which the negative battery plate is coated and which is composed of four components: a lead base, carbon, barium sulfate and lignosulfonate, at least two of said components being present at least in part as composite particles. Example 3 describes how a suspension of carbon black particles and barium sulfate nanoparticles are subjected to spray drying.

US 2006 0141162 A1 (EGUSA) has as its object a pigment dispersion, the dispersion containing carbon black and barium sulfate particles and a dispersant. Not disclosed are composite particles.

US 2019 0194470 A1 (OCI) relates to a method for preparing a carbon black of high resistivity through the surface treatment of the carbon black which exhibits conductivity, and a carbon black prepared by this method.

JP-A-2004/168963 (TOKAI CARBON) discloses a carbon black pigment modified by wet oxidation, reporting that conductivity of the modified carbon black is very low. However, a high OD requiring a high loading of carbon black pose the challenges of maintenance of a high level electric resistivity at a high loading level of carbon black.

While carbon blacks with modified surfaces are known from the state of the art, qualities found in the market are sensitive to high temperatures. Particularly post processing for display manufacturing requires temperatures of about 230° C. for about 30 minutes which leads to serious degradation of the organic groups attached to the surface of the carbon black particles.

Therefore the object of the present invention has been providing carbon black composites to fulfill the aforementioned key requirements like high optical density, high thermal durability, low electric conductivity at a high loading level of carbon black, a good processability, a low UV absorption and particularly a high level of bluish undertone.

A first object of the present invention refers to composite particle comprising or consisting of a solid core partially or entirely coated with at least one inorganic compound, wherein

Surprisingly it has been found that deposition of certain nano-sized inorganic compounds on the surface of carbon black particles improves color, bluish undertone, gloss, and particularly a thermal-durable color, bluish undertone, gloss, and decreases at the same time electric conductivity even at high loading levels of composite particles in contrast to the pure carbon black.

The new particles are well suited for uses in coating, inks and polymers where not only color is demanded, also bluish undertone is highly pursued. Therefore the particles may serve as color agents in coating and printing formulations which both blackness and bluish undertone are demanded, under special circumstances, paints have to survive a high temperature baking with well-maintained color properties. In fact, a very high loading of carbon black is added to pursue a high optical density and meanwhile, a same level on electrical insulation as organic polymer is required, which is not able to fulfill by normal carbon black. The new particles may also serve as non-conductive fillers in applications wherein both a high electrical resistivity and a high loading of carbon black after enduring a high temperature baking is required. The particles can be applied to black matrix compositions where surface resistivity and optical density are properties of high importance and thermal durability on these two properties as well.

Carbon Black Particles

Carbon black forming the solid core of the composite particles according to the invention is required to have functional groups such as carboxyl or hydroxyl groups on the surface thereof. Within the meaning of the present inventions examples of carbon black, include but are not limited to furnace black, gas black, thermal black, lamp black, but also carbon fibers, carbon plates, activated carbon, vitreous carbon, charcoal, graphite and combination thereof. The carbon black may be of the crystalline or amorphous type. The carbonaceous material can also be a waste product or by-product of carbonaceous material obtained by pyrolysis.

Carbon black core particles useful for the present invention may, for example, have primary particles sizes in the general range of from about 10 nm to about 250 nm, more preferably from about 10 nm to about 100 nm and most preferred from about 15 nm to about 50 nm.

The STSA of carbon black used in this invention is determined in accordance with ASTM D6556 (2004). The STSA surface area of these particles can be less than 400 m/g, and preferably less than 380 m/g, and the oil absorption number (OAN) of carbon blacks is determined according to ASTM D2414. The OAN of carbon black used in the composition preferably ranges from about 10 cc/100 g to about 500 cc/100 g, more preferably, from about 50 cc/100 g to about 300 cc/100 g.

The pH of a carbon black is determined based on DIN ISO 787/9 (1995). Suitably, the carbon black used herein may have a pH value of equal or less than 8.

The amount of the volatile components in the carbon black is determined from a residual weight of the carbon black after heating the carbon black at 950° C. for 7 min according to ASTM D1620-60. Suitably, the carbon black used herein may have a volatile by wt % not less than 2%, preferably not less than 5%, more preferably not less than 10%.

Furthermore, carbon black used for the present invention may include self-dispersed pigments and polymer-dispersed pigments. Self-dispersed pigments and stir-in pigments encompass those that have been chemically surface modified with a charge or an functional grouping. This chemical modification aids the pigment in becoming and/or substantially remaining dispersed in a liquid vehicle. The pigment can also be a polymer-dispersed pigment that utilizes a dispersant such as a polymer or an oligomer or a surfactant in the liquid vehicle. The pigment can also utilize a physical coating to aid the pigment in becoming and/or substantially remaining dispersed in a liquid vehicle.

Furthermore, the carbon black used for the present invention can be carbon black being oxidized by liquid-phase oxidation or gas-phase oxidation. The oxidizing agent may employ any reagent which is suitable for surface oxidation of carbon black in aqueous phase. The reagent may be hydrogen peroxide aqueous solution, nitric acid, sulfuric acid, hypochlorate, persulfate such as sodium and potassium persulfates, hypohalites such as sodium hypochlorite, ammonium persulphate, or percarbonate transition metal-containing oxidants such as permanganate salts, osmium tetroxide, chromium oxides, ceric ammonium nitrates; and mixtures thereof. The degree of oxidation may be adjusted by changing the concentration of the oxidizing agent, the oxidation temperature, the oxidation time, the amount of carbon black added to the oxidizing agent aqueous solution, and the like.

When utilizing gas-phase oxidation, the carbon black is oxidized by contacting the carbon black with ozone, air, or the like at an appropriate temperature. Gas-phase oxidation has an oxidizing power lower to some extent than liquid-phase oxidation, but has an advantage in that drying is unnecessary and the operation is easy.

As the result of said oxidation process various functional groups may be present on the surface of the carbon black and those features surface-bound polar, ionic or ionizable groups, such as hydroxyl, phenol, lactone, chinone, ketone, anhydride, lactone, peroxidic, ether and/or carboxylic acid groups, sulfate, sulfonate, phosphate, phosphonate, nitrate, carboxylate, including also active alkylene groups, and the like.

Inorganic Compounds

The inorganic compounds are defined by their surface charge as explained above. Preferably the surface charge—also called zeta potential, determined for example by a Malvern Zeta Sizer—ranges from about −30 to about +30 mV and preferably from 0 to about +30 mV. These inorganic compounds can be treated with organic surface modifying agents in order to shift their surface charge into the aforementioned range.

The inorganic compounds are used for coating the modified carbon black solid core by deposition, either fully or in part. They do neither substantially absorb visible light nor do they interact with other components in the end-use application.

In another preferred embodiment the inorganic compounds are selected from alkaline earth salts, more preferably from alkaline earth sulfates. The most preferred inorganic compound is barium sulfate, for example a barium sulfate nanoparticle with a diameter of 5-100 nm.

Along with said alkaline earth salts sulfates, carbonates, nitrates, carboxylates and oxides of metals chosen from the second main group of the periodic system can be added.

Further on it is desirable that the inorganic compounds are smaller than carbon black solid core particles. The average size of the inorganic compounds ranges from about 5 to about 100 nm and more preferably from about 5 to about 50 nm. In accordance with the present invention, the inorganic compounds may form a non-continuous coating by a discrete particle form and can be observed and measured by electron microscopy such as transmission electron microscopy.

The amount of inorganic compounds is typically at least 50 wt.-percent, preferably about 60 to about 80 wt.-percent and more preferably from about 65 to about 75 wt.-percent—calculated on the total weight of the composite particle. The inorganic compounds can be amorphous or crystalline and the shape of the particles can be spherical, oval, rod-like or platelet or equiaxial. Preferably, the inorganic particles are spherical or oval.

It is desirable to generate a discrete distribution of the inorganic compounds robustly anchored on the surface of carbon black solid core particles. The inorganic particles will be attracted to the surface of carbon black solid core by charge driven force.

Organic Surface Modifying Agents

Agents suitable for modifying the surface of the composite particles encompass aromatic molecules such as for example 4-chloro benzoic acid or amino acids, such as for example N-lauroyl lysine. Also silane compounds are able to modify the surface of the composite particles accordingly.

Manufacturing Process

Another object of the present invention relates to a process for preparing the composite particles of claim, comprising or consisting of the following steps:

In particular, the present invention discloses

Suitable solvents encompass water and alcohols such as the aliphatic C-Calcohols, preferably ethanol. Preferably, the solvents for the first and the second dispersion are the same.

The concentration of the oxidized carbon black in the first dispersion is typically prepared not less than 10 wt.-percent, preferably to not less than 20 wt.-percent and more preferably to not less than 30 wt.-percent. The slurry is usually purified using a separation membrane such as an ultrafilter (UF) membrane, a reverse osmosis (RO) membrane, or an electrodialysis membrane to remove salts.

In case water is used as the solvent, the dispersion of the oxidized carbon black can be subjected to neutralization to improve its stability. For example, the pH of the dispersion can be controlled to be alkaline, for example in a range from 8 to 12 or from 8.5 to 11.0 such as from 8.5 to 10.5, from 8.5 to 10.0, from 8.5 to 9.8, from 9.0 to 11.0, from 9.0 to 10.0, from 9.0 to 9.8, from 9.5 to 11.0, from 9.5 to 10.5, from 9.3 to 9.8, from 9.3 to 11.0, from 9.3 to 10.5 or from 9.3 to 10.0 or to a range between any of the recited values. Control of the pH in the manufacture of the solid pigment preparation, e.g. to any of the afore-mentioned ranges, may employ such as amine and protonated amine groups such as amino alcohols, 2-amino-2-methyl propanol, 2-di-methyl-amino ethanol, 2-amino-2-methyl-1,3-propanediol, 2-amino-1-butanol, diethylethanolamine, 2-(diisopropylamino)ethanol, and 2(dibutylamino)-ethanol; or amines such as triethylamine; diisopropylamine or an aqueous ammonia solution. The pH of the dispersion can for example be measured with a pH meter such as a Metrohm 780 instrument.